In a flow system different problems caused by changes in the flow can damage a pressure sensor like the one in this invention; especially the sealing diaphragm can be damaged. The problems causing damage can be cavitations or pressure peaks or start up liquid jets.
In flow systems where sudden changes in the flow can occur for example by closing a valve, it is well known that cavitations related to “liquid hammer” can give huge pressure changes which can cause damage to pressure sensors especially to the sealing diaphragm. When a valve suddenly is closed the flow medium decelerates, creating cavitations forming gas pockets and when the flow medium returns, it will result in huge pressure changes. If these cavitations are close to a pressure sensor, the change in pressure will have the effect that liquid will be hammered against the sensor causing possible damage to the sealing diaphragm or to the micromechanical elements covered by the sealing diaphragm.
Pressure peaks, occurring in the flow system due to changes in the flow, can also damage the diaphragms in a pressure sensor. This is however mostly a problem for the measuring diaphragm inside the pressure element. The measuring diaphragm can be made of silicon or steel. Measuring diaphragms made of steel are more sensitive to pressure peaks than measuring diaphragms made of silicon.
When a flow system is empty and then filled with the flow medium; start up jets can occur, when the flow medium enters the empty pressure sensor with high speed. The start up jets can damage the sealing diaphragm.
The document U.S. Pat. No. 5,509,312 describes a diaphragm pressure sensor with integrated anti-shock protection means. The diaphragm pressure sensor can withstand relatively large shocks without the shocks resulting in the diaphragm bursting or in any damage to the sensor. One embodiment is a passage with a strait hole, where the strait hole works as a low pass filter cutting off the high pressure peaks.
Another prior art is an existing design for a pressure sensor, where a nozzle is welded into the pressure-connection inlet (FIG. 1). There is a relatively long distance between the nozzle and the sealing diaphragm. The long distance is necessary because the nozzle-hole is straight. If the distance between the nozzle and the sealing diaphragm is shorter, there is a risk a damaging liquid-jet in the start-up situation will damage the sealing diaphragm.
Further more the existing solutions in form of pulse snubbing restriction elements are difficult to mount, because they are placed in the fluid inlet. Extra effort is necessary to be sure the restriction element is securely mounted. The restriction element can be welded into the inlet or fastened in other ways. If the restriction element is damaged, it can fall out and disappear.